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Customised symphysio fundal height chartsK H B Shamawarna1, I M R Goonewardene1, Y A G Perera3

(Index words: customised symphysio fundal height charts)

AbstractObjectives To evaluate the feasibility, applicability andthe value of customised symphysio fundal height (SFH)charts developed for women of Indian origin in the UnitedKingdom (UK: CSFH – In chart) and women of Africanorigin in the UK (CSFH – Af chart) in detecting fetal growthrestriction and predicting low birth weight (LBW) of theneonate in a Lankan population, and to compare theseresults with the results obtained from the SFH chartcurrently used in Sri Lanka (FHB chart) and another SFHchart which uses a range of plus or minus 2-3 cm of thevalue of the gestational age in weeks as the referencerange (GA 2 to 3 cm chart).

Methods Pregnant women (n = 416) with confirmedperiods of gestation (POG) of <22 weeks and having asingleton fetus and with no obstetric complications, hadtheir age, parity, POG and Body Mass Index (BMI)documented. Their SFH were measured at four weekly,fortnightly and weekly intervals between 20 - 28, 28 - 36and 37 - 41 weeks respectively and plotted on the CSFH– In chart, CSFH – Af chart, FHB chart and the GA 2 to 3cm chart. The gestational age at delivery and the birthweight were recorded. Pre term deliveries were excludedleaving 401 participants for analysis.

Results There were 164 (39.4 %) primigravidae, 76 (18.9%) had low BMI and 71 (17.7 %) had a high BMI. MaternalBMI at booking was positively correlated to the birthweight of the baby but not the parity. In detecting LBW atterm, the CSFH – In chart had the best sensitivity,specificity, positive predictive value, negative predictivevalue, and the likelihood ratios. Of the two non customisedcharts the GA 2 to 3 cm chart was better than the FHBchart.

Conclusions Until a customised SFH chart is developedfor Sri Lanka, the CSFH – In chart or the GA 2 to 3 cmchart should be used for antenatal monitoring of fetalgrowth.

Ceylon Medical Journal 2012; 57: 159-165

IntroductionA fetus which is below the 10th centile for its expected

gestational age specific birth weight is generally considered

1Obstetrics and Gynaecology Unit, Teaching Hospital, Mahamodara, Galle, 2Department of Obstetrics and Gynaecology,University of Ruhuna, Faculty of Medicine, Galle, Sri Lanka.

Correspondence: IMRG, e-mail: <malikg@eureka.lk>. Received 18 May and revised version accepted 9 August2012. Competing interests: none declared.

to be small for gestational age (SGA) [1]. However, it isimportant to differentiate between a healthyconstitutionally small fetus with no associated adverseoutcomes from a fetus that has pathological intra uterinefetal growth restriction (FGR) with associated perinataland long term adverse outcomes [1,2]. The measurementof the symphysio fundal height (SFH) has been shown tohave specificities of up to 94% in detecting a SGA fetus,but the sensitivities reported vary from 84% to 27% [3,4].

The low sensitivity, high false positive rates,significant intra and inter observer variations make SFHper se an unreliable index in detecting SGA [4,5]. Althoughthe mean value of SFH in cm plus or minus 2 cm inCaucasian populations has been found to approximatethe gestational age in weeks between 20 - 36 weeks ofgestation very often it is approx 2 cm less than the valuein weeks [6]. Furthermore between 36 - 40 weeks the rangecould be as large as plus or minus 3 cm and at 40 weeksthe range could be as large as plus or minus 4 cm [6]. Theinterpretation of a single SFH measurement in centimetresto be corresponding to the gestational age in weeks (ie. apoint to point conversion) is not logical. Serial ultrasoundmeasurement of growth velocity using fetal abdominalcircumference and estimated fetal weight have been shownto be the best indices to predict FGR [7]. Therefore serialSFH measurements plotted on a reference chart may be auseful screening tool to detect FGR [8,9].

SFH measurements have been used for more thanfour decades and its limitations, especially on account ofthe wide variation in body stature and lengths of women’sabdomens, have been appreciated from its inception [10].The main non pathological factors which affect the birthweights are gestational age, maternal height, maternalweight at booking, parity and ethnic group [11].

Maternal age appears to have no significant effectwhen parity is controlled for [11]. Paternal height, unlessextreme, appears to have a relatively minor effect. Using adata set of around 40,000 ultrasound dated pregnanciesand adjusting for the main non pathological factors whichaffect fetal growth, a Term Optimal Weight (TOW) whichis the weight the baby is predicted to achieve in theabsence of pathological influences has been calculated inNottingham UK, Australia, New Zealand and the UnitedStates of America [11-14].

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Using the TOW, a proportionality curve can be drawnto demonstrate how this weight is expected to be reachedin a normal pregnancy. Then, individually adjusted(customised) Gestation Related Optimum Weight (GROW)charts can be obtained to plot the serial SFH measurementsand monitor fetal growth [14]. These customised SFHcharts have been found to be better in antenatal fetalmonitoring and detecting SGA fetuses [24, 25]. Thereforeserial measurement of SFH plotted on customised SFHcharts has been recommended [1,15,16]. SFH chartsdeveloped in the UK, Australia and New Zealand, andcustomised according to ethnicity, parity and BMI areavailable as the computer software GROW which can bedownloaded free of charge for personal or institutionaluse [17]. These charts show the Term Optimal Weightcalculated for 280 days and they are individually adjusted(customised according to ethnicity, parity and BMI). Thesecharts include proportional growth curves together withthe 10th and 90th centile lines showing how this weight isexpected to be reached during a normal pregnancy.Longitudinally plotting the SFH on these charts duringthe pregnancy enables the monitoring of fetal growth.The objective of the current study was to compare thefollowing SFH charts in the detection of low birth weightbabies (LBW = <2.5 kg) at term (>37 weeks gestation):

1. Customised SFH Charts developed for women of Indianorigin in the UK (CSFH – In: Figures 1, 2 and 3)

2. Customised SFH Charts developed for women ofAfrican origin in the UK (CSFH – Af: Figure 4)

3. SFH Chart using the gestational age plus or minus 2cm from 20 - 36 weeks and gestational age plus orminus 3 cm from 36 - 40 weeks as the reference range(GA 2 to 3 cm Chart: Figure 5)

4. The SFH Chart included in the Lankan PregnancyRecord Card (FHB Chart: Figures 6)

Figure 1. Customised antenatal growth chart.

Figure 2. Customised antenatal growth chart.

Figure 3. Customised antenatal growth chart.

Figure 4. Customised antenatal growth chart.

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Figure 5. gestational age 2 to 3 cm SFH chart. Figure 6. FHB chart

Figure 7. Symphysio fundal height chart - customized according tobody mass index

Red = 10th and 90th centiles of symphysio fundal height chart customisedaccording to a body mass index of 17.1 kg/m2

Black = 10th and 90th centiles of symphysio fundal height chart customisedaccording to a body mass index of 21.8 kg/m2

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The mean birth weight of a Lankan newborn in theGalle District is estimated to be approx. 2.9 kg and 20.8%of babies are considered to be of low birth weight definedas <2.5 kg [26]. In the CSFH – In chart the 50th centile ofthe birth weight of a baby born at 40 weeks to aprimigravida having a height of 140 cm, booking weight40 kg and BMI of 20.4 kg/m2 is approximately 2.9 kg and inthe CSFH – Af chart the 50th centile of the birth weight ofa baby born at 40 weeks to a primigravida having a heightof 148 cm, booking weight 45 kg and BMI of 20.5 kg/m2

is approximately 2.9 kg [17]. This was the rationale forincluding the CSFH – In and the CSFH – Af customisedSFH charts in the current study.

MethodsApproval was obtained from the Ethical Review

Committee of the Faculty of Medicine, University ofRuhuna and informed written consent was obtained fromall the participants recruited for the study. The normalrange of BMI is considered to be 18.5 - 24.9 kg/m2 in thenon pregnant state [18]. Considering three categories ofBMI (< 18.5 kg/m2 = low, 18 .5 - 24.9 kg/m2 = normal and >25 kg/m2 = high) and three categories of parity (1, 2 and >2) as the possible variables, there would be nine possiblecategories of women in the study. Therefore assumingthat 85% of women would fit the standard curve with anormal deviate of 5%, the minimum sample size requiredfor each category was calculated to be 46 resulting in atotal sample size of 414 [19]. In a study carried out inKegalle the mean birth weight of Sinhalese babies born atterm was reported to be 2.85 (sd 467g) [20]. Since a largemajority of women who reside in the Galle district areSinhalese, the population standard deviation in Galle canbe assumed to be similar to that reported in Kegalle.Therefore, the minimum sample size required to estimatethe mean birth weight with a normal deviate of 5% and anaccuracy of 50 g in a population having a standarddeviation of 500 g, was calculated to be 384 [19]. It wasdecided to adopt the larger sample size of 414.

Pregnant women (n=468) who presented for antenatalcare at the Teaching Hospital, Mahamodara, Galle (THMG)during the period 1 August 2007 to 30 April 2008 withperiods of gestation (POG) of <22 weeks and not havinganaemia, hypertension, diabetes mellitus, cardiac disease,hydramnios or multiple pregnancy, had their POGconfirmed by ultrasound scan if a dating scan had notbeen carried out earlier. Their age, parity, height and weightwere documented. The earliest recorded weight duringthe current pregnancy was used to calculate the BMI.Women who developed anaemia, hypertension, diabetesmellitus, hydramnios, an abnormal lie or death in-utroduring the pregnancy, and those who defaulted prenatalclinic visits and therefore had less than four longitudinalSFH measurements, were excluded from the study. Thisresulted in 52 women being excluded from the study,leaving 416 for analysis.

Two customised charts were obtained for each womanafter incorporating each woman’s basic informationincluding parity, height and weight and entering Indianand African as ethnicity in the GROW computer software[17]. This enabled the downloading of one CSFH – In andone CSFH – Af chart respectively for each woman. Eachwoman was also provided with a printed out FHB chartand a GA 2 to 3 cm chart. All four charts were incorporatedin to the patient held antenatal records which she carriedwith her until the delivery.

Having identified the fundus of the uterus, using anon elastic tape with the centimetre markings facing thematernal abdomen, the SFH was measured from the top ofthe uterine fundus to the top of the symphysis pubis alongthe longitudinal uterine axis at each antenatal clinic visitand plotted on all four SFH charts. The data were alsorecorded and kept confidentially in an ongoing computerdata base.

The SFH measurements were carried out mainly bythe first author (n=1359) and if the first author wasunavailable, by the on call senior house officer (n=179) inan opportunistic manner during the routine prenatal followup. At the time of SFH measurement the first author andthe on call senior house officer were blind to the women'sPOG .

Duplicate SFH measurements were also obtained in400 participants by other house officers who were blindto the POG. All the women had routine antenatal care andhad their SFH measured at four weekly intervals,fortnightly and weekly intervals between 20 - 28, 28 - 36and 37 - 41 weeks respectively and plotted on the CSFH –In chart, CSFH – Af chart, FHB chart and the GA 2 to 3cm chart. If any SFH measurement was found to be outsidethe reference range in any of the non customised SFHcharts in any woman at any time, she was reviewed by thesecond or third author and managed appropriately.

Serial SFH measurements were used to predict LBWin all the charts. If the last SFH measurement was lessthan the cut off value in any specific chart, it wasconsidered as “test positive” for that particular chart,irrespective of the previous SFH measurements obtainedfor that particular patient. If the last SFH measurementwas within the normal range in any specific chart, andboth the two previous SFH measurements were was lessthan the cut off value in any specific chart, this was alsoconsidered as “test positive” for that particular chart. Ifthe last SFH measurement was within the normal rangein any specific chart, and only one previous SFHmeasurement was less than the cut off value in any specificchart, this was considered as “test negative” for thatparticular chart.

The gestational age at delivery and the birth weightwere recorded. The sensitivity, specificity, positivepredictive value (PPV), negative predictive value (NPV),likelihood ratio of a positive test and the likelihood ratioof a negative test in the detection of a LBW baby at term,

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Table 1. Basic characteristics of study population (n=416)

Range Mean 95% Confidence Interval

Age – years 16 - 45 27.5 26.9 - 28.1Body mass index – kg/m2 13.5 - 33.7 21.8 21.5 - 22.2Period of gestation at delivery – days 242- 293 275 273.3 - 276.5Birth weight of babies delivered at term (n=401) 1670 - 4450g 2990g 2945 - 3035gBirth weight of babies delivered pre-term (n=15) 1630 - 2820g 2230g 2067 - 2393gParity : range 1 -7 median (IQR) 2 (2)Primigravidae (%) 164 (39.4)Pre-term deliveries (%) 15 (3.6)

IQR = inter quartile range

Table 3. Association of parity and birth weight

Parity 1 2 3 4 Total(n = 154) (n = 114) (n = 79) (n = 54) (n= 401)

Birth weight < 2.5 kg 1 8 1 3 1 1 6 4 8( 11.6 % ) ( 11.4 % ) ( 13.9 % ) ( 11.1 % ) ( 11.9 % )

Chi-square = 0.4, p = 0.9, r2 = 0.004, p = 0.2

were calculated and compared among the four SFH chartsused in the current study.

ResultsOf the 416 participants recruited for the study, 164

(39.4%) were primigravidae, 76 (18.9%) had low BMI and71 (17.7%) had high BMI (Tables 1 and 2). The SFHmeasurements taken by two observers were highlycorrelated and no significant inter observer variation wasseen. (Reliability Coefficient Alpha = 0.9774, p <0.0001).Of the 416 participants recruited for the study 15 (3.6%)had preterm deliveries and only the balance 401 underwentfurther analyses. The 401 babies born at term (37 -42 weeksgestation) had a mean birth weight of 2990 g (95% CI 2945- 3035) (Table 1). No significant association was seenbetween maternal parity and birth weight of the baby(Table 3).

The maternal BMI at booking was positivelycorrelated to the birth weight of the baby (r2 = 0.016, p =0.012 on simple linear regression analysis and r2 = 0.017, = 0.119, p = 0.02 on logistic regression analysis combining

the effects of parity and BMI). The mean BMI of the low,normal and high BMI groups were 17.2 kg/m2 (95% CI17.0 - 17.4), 21.8 kg/m2 (95% CI 21.6 - 22.0 ) and 27.6 kg/m2 (95% CI 27.1 - 28.1) respectively. The mean birth weightin the low BMI group (2861 g, 95% CI 2783 - 2938) wassignificantly higher than the mean birth weight in thenormal BMI group (3043 g, 95% CI 2991 - 3094, p < 0.01).However, only a non significant increase of approx. 50 gwas noted between mean birth weight of the high BMIgroup and the normal BMI group (Table 4).

In almost all the participants in whom the final SFHvalue was below the cut-off point for any particular chart(and therefore considered as being a ‘test positive’ fordetection of LBW), two or more previous serial SFHmeasurements were below the respective cut-off pointsfor the particular chart. In the detection of a LBW at term,the CSFH – In chart had the best sensitivity, specificity,PPV, NPV, and the likelihood ratios of a positive test and anegative test. Of the two non customised charts the GA 2 to 3 cm chart was better than the FHB chart, becausealthough the FHB chart had a specificity of 100% it hadzero sensitivity (Table 5).

Table 2. Distribution of parity and body mass index (n= 401)

P1 P2 >P2 Total (%)

BMI <18.5 kg/m2 3 8 1 9 1 9 76 (18.9)BMI 18.5 - 24.9 kg/m2 9 6 7 0 8 8 254 (63.3)BMI >25 kg/m2 2 0 2 5 2 6 71 (17.7)Total 154 114 133 401

BMI = body mass index, P = ongoing pregnancy

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Table 4. Association of maternal body mass index and birth weight

BMI <18.5 kg/m2 BMI 18.5-24.9 kg/m2 BMI >25 kg/m2

(n=76) (n=254) (n=71)

Range 14.1 - 18.4 18.5 - 24.9 25 - 33.7Mean 17.2 21.8 27.6SD 0.9 1.7 2.295% CI 16.9 - 17.4 21.6 - 22 27.1 - 28.1Birth weight (g) Range 2110 - 3570 1850 - 4350 1670 - 4450 Mean 2861* 3043* 3094 SD 343 422 545

95% CI 2783.8 - 2938.2 2991.1 - 3094.9 2967.2 - 3220.8

Simple linear regression: r2 = 0.016, p = 0.012Logistic regression of BMI and parity vs birth weight:r2 = 0.017, for parity = 0.037, p = 0.461, and for BMI = 0.119, p = 0.019* = p <0.01

Table 5. Validity of Simphysio Fundal Height Charts in the detection and exclusion of a low birthweight (< 2.5 kg) baby at term (> 37 weeks gestation) (n= 401)

CSFH – Af CSFH – In GA ± 2 to 3 cm FHB

Sensitivity 54.2% 62.5% 81.2%(39.3 - 68.4) (95%CI:48.5-74.7) (95%CI:66.9-91.0) (95%CI:0-9.2)

Specificity 96.9% 98.5% 86.9% 100% (94.3 - 98.3) (95%CI:96.4 - 99.5) (95%CI:82.9-90.2) (95%CI:98.6-100.0)

PPV 70.3% 87.5% 45.8% NaN(52.8 - 83.6) (95%CI:72.3 - 95.3) (95%CI:35.1-57.0)

NPV 93.4% 94.2% 97.1% 88% (90.8 - 96.1) (95%CI:91.2 - 96.3) (95%CI:94.77-98.6) (95%CI:84.3-90.9)

LR Pos 17.4 43.1 6.2 (9.5 - 32.9) (95%CI:17.6 - 105.4) (95%CI:4.6-8.4) NaN

LR Neg 0.48 0.38 0.21 1 (0.35 - 0.64) (95%CI:0.27 - 0.53) (95%CI:0.12-0.39) (95%CI:1-1)

NaN = calculation cannot be performed because the values entered include one or more instances of zeroPPV = positive predictive valueNPV = negative predictive valueLR Pos = likelihood ratio for a positive testLR Neg = likelihood ratio for a negative test

DiscussionOf the customised charts the CSFH – In chart was

better than the CSFH – Af chart in the detection andexclusion of a LBW baby at term in the study population.This could be explained by the fact that in comparisonwith Africans, Indians would be expected to be ethnicallyand genetically closer and similar to Lankans.

Although BMI and parity are both known to affectthe birth weight of the baby, the influence of BMI on thebirth weight of the baby has been shown to be more thanthat of parity [17,20-21]. In the current study, low BMIsignificantly affected the mean birth weight while no

significant effect was noted with parity. Since no significantincrease of mean birth weight was noted between thenormal BMI group and the high BMI group, forconvenience a SFH chart customised according to low(<18.5 kg/m2) and normal (18.5 - 24.9 kg/m2) could bedeveloped for Sri Lanka. Until such a chart is developed,the mean BMI for these two groups (17.2 kg/m2, 95% CI17.0 - 17.4 and 21.8 kg/m2, 95% CI 21.6 -22.0) could beentered into the CSFH – In chart to generate one ReferenceChart customised according to BMI (Figure 7). This couldbe easily incorporated in to the Maternal PregnancyRecord and be used by even family health workers inperipheral antenatal clinics. This chart would be similar to

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the growth chart used for monitoring a child’s growth.The only difference would be that in the customised SFHchart the interpretation of the serial SFH measurementswould depend on the maternal BMI at booking.

Ideally a customised SFH chart should be developedfor Sri Lanka. Until such a chart is developed, in centreswhere computers and internet connectivity is available,the CSFH – In chart could be used for better monitoring ofpregnant women with a view to improving the detectionand exclusion of SGA fetuses and LBW babies at delivery.In the centres where computers and internet connectivityare not available, the GA 2 to 3 cm chart should be usedin preference to the FHB chart.

A symphysio fundal height chart customisedaccording to two groups, low and normal body massindex categories at booking, should be developed for SriLanka. Until this is developed, one Reference Chartcustomized according to BMI or the gestational age 2to 3 cm chart could be used. If computers and internetconnectivity are available, the customized symphysiofundal height charts used for Indians in the UK may beused.

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